Generally, as shown in FIG. 1, a CRT includes a panel 10 having a fluorescent layer 2 on the inner side thereof, a shadow mask frame assembly 4 fixed to the inner side of the panel 10, being separated from the fluorescent layer 2 by a predetermined distance, an electron gun 7 and a deflection yoke 5, installed at a neck portion 6 and a cone portion 8, respectively. Here, the shadow mask frame assembly 4 installed in the panel 10, as shown in FIG. 2, includes a shadow mask 3 having a hole portion 3a with a plurality of electron beam passing holes H and a concave skirt portion 3b extending from the edge of the hole portion 3a, and a frame 9 coupled with the skirt portion 3b for supporting the shadow mask 3. Also, the shadow mask frame assembly 4 is coupled with a spring (not shown) fixed on the side of the frame 9 and a stud pin (not shown) fixed on the inner side of the panel, thereby separating the shadow mask 3 from the fluorescent layer 2 by a predetermined distance.
According to the CRT having the above structure, after the electron beam emitted from the electron gun 7 is selectively deflected by the deflection yoke 5 according to the scanning position of the electron beam on the fluorescent layer 2, the electron beam passes through the electron beam passing holes H of the shadow mask 3 supported by the frame 9 and reaches the fluorescent layer, thereby forming an image. Here, only 15.about.30% of the electrons pass through the electron beam passing holes H of the shadow mask. The remaining electrons which could not pass through the electron beam passing holes H collide with the hole portion 3a of the shadow mask 3, so that the shadow mask 3 and the frame 9 supporting the shadow mask 3 are heated, which causes a doming phenomenon of the shadow mask 3.
Due to the doming phenomenon of the shadow mask 3, the location of the electron beam passing holes H in the hole portion 3a of the shadow mask 3 is changed, so that the electron beam emitted from the electron gun 7 is not correctly incident on a fluorescent point of the florescent layer 2.
To solve this problem, according to a conventional method, the interval between the fluorescent layer 2 and the shadow mask 3 is controlled by moving the shadow mask 3.
However, by such a method, the doming phenomenon is suppressed only when the shadow mask 3 is completely domed through a thermal expansion thereof. Thus, decreased resolution due to an initial doming phenomenon cannot be prevented.
In order to prevent the doming phenomenon, a shadow mask made of invar (invariable steel) is disclosed in U.S. Pat. Nos. 4,665,338 and 4,420,366. The conventional shadow mask made of invar can resist the thermal expansion. However, the use of invar has disadvantages in cost and processing.
As another method for reducing the thermal expansion ratio of the shadow mask, depositing a material having a low thermal expansion ratio, such as lead borate, on the surface of the shadow mask is known.
As still another method for preventing the doming phenomenon, depositing an insulating material on the surface of the shadow mask is widely known. This method prevents the transfer of heat generated by the electron beam to the shadow mask, wherein ceramic is mainly used as the insulating material.
As still yet another method, a material having a high thermal radiating coefficient is applied to the surface of the shadow mask or the shadow mask is darkened, to increase the thermal radiating ratio. Also, depositing an aqueous suspension including an electron reflection material on the surface of the shadow mask has been disclosed by Phillips.
Generally, the thermal insulating material, thermal radiating material, electron reflecting material, etc. are applied to the surface of the shadow mask by a spray method or a sputtering method. According to the spray method, where an aqueous suspension is sprayed on the mask surface via a nozzle, some of the holes formed on the shadow mask become clogged even if the spray process is precisely controlled, and the mask surface coating produced by this method is not even.
On the other hand, according to the sputtering method, wherein gas ions generated during a glow discharge collide with a target cathode and then the atoms emitted from the target coat to the substrate of an anode, the coated layer is thin and expensive deposition equipment is required.
In order to solve the defects of the above described coating methods, a new coating method using screen printing is disclosed.